BackgroundStandard mitral valve replacement (MVR) in patients with chronic mitral regurgitation results in consistent reductions in resting postoperative ejection fraction. This has been attributed to removal of the low-impedance ejection pathway into the left atrium or to disruption of the chordal apparatus. Mitral valve repair (MVP) does not reduce ejection fraction at rest. However, whether MVP confers any advantages with regard to dynamic left ventricular performance has not been investigated. The aim of this study was to directly compare standard MVR with MVP and to determine their respective influences on ventricular ejection performance during bicycle exercise.Methods and ResultsTen consecutive patients with pure chronic mitral regurgitation who underwent MVP and 10 patients matched for age, sex, and preoperative ejection fraction who underwent standard MVR for pure chronic mitral regurgitation performed symptom-limited, graded upright bicycle exercise with simultaneous Doppler and quantitative two-dimensional echocardiography. Patients with MVP had significantly greater rest (55 ± 12%) and exercise 63±11%) ejection fractions than matched patients with MVR 40±13% [P< .0001] and 42±17% [P< .005], respectively). End-systolic circumferential wall stress was significantly lower at rest (190±36 versus 244±46;P< .03) and at peak exercise 231±46 versus 300±52;P< .02) in patients with MVP. At peak exercise, left ventricular shape was significantly more spherical in patients with MVR than those with MVP 1.84±0.31 versus 2.45±0.59;P< .02).ConclusionsMVR with chordal transection resulted in significant reductions in rest and exercise ejection fraction. This was caused in part by a significant increase in end-systolic circumferential wall stress. MVP resulted in improved rest and exercise ejection indexes, primarily due to a marked reduction in end-systolic stress and maintenance of a more ellipsoidal chamber geometry.